1. Technical Field
The present invention relates to crankcase ventilation systems. More specifically, the present invention relates to an air intake channel in communication with intake channels in the cylinder head of a supercharged internal combustion engine for preventing overpressure in a crankcase.
2. Background Information
In an internal combustion engine, it is difficult to provide piston ring seals between the pistons and their surrounding cylinder walls that provide a complete seal between the combustion chambers and the engine crankcase in normal engine operation, as opposed to engine braking. A certain amount of combustion gases, referred to as xe2x80x9cblow-byxe2x80x9d, almost always leaks past the piston rings into the engine crankcase. To avoid excessively high overpressure developing in the crankcase due to blow-by, the crankcase must be ventilated, wherein these gases are diverted thereby permitting only a low overpressure in the crankcase.
A crankcase requires ventilation to atmospheric pressure. However, for environmental reasons, the simplest and cheapest solution - ventilating the crankcase directly to the surrounding atmospherexe2x80x94is not acceptable. Instead, blow-by must be returned to the engine combustion chambers, which can be accomplished by mixing them with intake air in the intake manifold. The simplest solution for mixing the gases is to connect the evacuation channel from the crankcase to the intake manifold at a point before the charging unit, since there is substantially atmospheric pressure from the air intake filter to the charging unit. Still, even when using some form of oil separator, a certain amount of missed oil accompanies blow-by out of the crankcase and into the charging system. This oil is collected in the charging system and, depending on the amount of oil and the temperature, can disturb the charging system functioning.
Oil collecting in the charging system can be avoided by connecting the evacuation channel after the throttle. However, when connected there, especially at low loads, a pronounced sub-atmospheric pressure occurs that is undesirable for several reasons. Also, crankcase gases cannot be evacuated to this location when the engine is supercharged. This can be solved by creating two evacuation channels, one before the charging unit and one after the throttle. The evacuation channel after the throttle is connected to the intake manifold via a constriction and non-return valve, thereby preventing flow in the direction away from the intake manifold. However, it is difficult to achieve balance in such a system both for suction engines, which always have sub-atmospheric pressure in the intake manifold, and supercharged engines, which have sub-atmospheric pressure in the intake manifold at low loads and overpressure at high loads.
In one crankcase ventilation system for supercharged engines, the evacuation channel to the intake manifold before the charging unit contains a pressure regulator for maintaining an essentially constant pressure corresponding approximately to atmospheric pressure in the crankcase. At high loads, gas flows through this evacuation channel to the intake manifold on the suction side of the turbo unit. Since there is overpressure in the intake manifold downstream of the throttle, the non-return valve in the other evacuation channel is closed so that no air can be forced back into the crankcase. At low load and sub-atmospheric pressure in the intake manifold downstream of the throttle, blow-by flows from the crankcase via the non-return valve and the constriction to the intake manifold. At the same time under certain operating conditions, air is pulled via the pressure regulator from the intake manifold upstream of the charging unit to the intake manifold downstream of the throttle. This exchange between hot gas flowing in one direction and cold air flowing in the other direction causes condensation, with the risk of frost blockage in cold weather. To avoid this problem, a heating coil with hot coolant therein can be placed around the evacuation channel upstream of the throttle. However, such an installation is expensive.
Accordingly, there is a need for a cost-effective way of ventilating a crankcase without venting blow-by to atmosphere. Further, there is a need for ventilating a crankcase incorporating blow-by into the crankcase without collecting oil in the crankcase. There is also a need for incorporating blow-by into the crankcase without causing condensation.
The present invention provides a supercharged internal combustion engine with pressure-regulated crankcase ventilation whereby the above described disadvantages are removed. This is achieved according to the invention in an internal combustion engine having a cylinder block, a cylinder head, a crankcase containing oil, and an air intake channel in communication with intake channels in the cylinder head. The engine further has a separator for separating oil out of evacuated blow-by gas.
The air intake channel is connected to a compressor or charge unit, and has a throttle downstream of the charge unit. The air intake channel has at least two evacuation channels and at least two pressure regulators. A first evacuation channel joins the crankcase to the air intake channel at a point downstream of the throttle for evacuating blow-by gases from the crankcase. This first evacuation channel communicates with a first pressure regulator arranged to maintain an substantially constant pressure in the crankcase. A second evacuation channel connects the crankcase to the air intake channel at a point on the suction side of the charge unit. This second evacuation channel communicates with a second pressure regulator arranged to maintain at least an approximately constant pressure in the crankcase. Both evacuation channels are coordinated with a valve or valve means that is disposed to limit or prevent gas flow in the direction from the intake channel towards the crankcase.
By virtue of the invention there is achieved a pressure-regulated crankcase ventilation both for suction engine operation, i.e., for low load operation, and for supercharging, i.e., for high load operation. During suction engine or low load operation, substantially all of the crankcase gas flows through the first evacuation channel to the intake manifold downstream of the throttle. This is due to the valve means in the second evacuation channel preventing or limiting the flow of fresh air in the opposite direction, i.e., to the crankcase. When the intake manifold is charged with overpressure, then substantially all the crankcase gas goes through the second evacuation channel to the intake manifold on the suction side of the charge unit. This is due to the valve or valve means in the first evacuation channel preventing or limiting the flow from the intake manifold to the crankcase.
The valve or valve means in the evacuation channels can be either simple check valves that completely block flow to the crankcase, or valves that prevent a high flow in the direction from the crankcase and a limited flow, or calibrated leakage, in the opposite direction. The advantage of the latter solution is that the risk of creating unacceptably low pressure in the crankcase when engine braking is eliminated. Since in this case there is no combustion producing blow-by gases, and the sub-atmospheric pressure in the intake manifold after the throttle is at a maximum when the throttle is closed, the sub-atmospheric pressure will otherwise cause gas to flow in the opposite direction, i.e., from the crankcase past the piston rings into the combustion chamber and out through the exhaust manifold. Under less favorable conditions, this reversed gas flow could lead to the crankcase pressure being so low that air would be sucked via the crankshaft seals into the crankcase from the surrounding atmosphere since the sealing lips of the seals are turned to seal against overpressure in the crankcase and not against overpressure on its outside. This can result in sucking in contaminants, causing damage to bearings, pistons and cylinder linings.
By the flowing of air from the surrounding atmosphere to the crankcase at a calibrated leakage through the valves allows selection of a pressure in the intake manifold which is so low that the engine does not produce any natural blow-by gas. Natural blow-by gas occurs when the average pressure above the piston is lower than the average pressure below the piston. This situation can occur during engine braking in combination with extremely low intake pressure. Despite the fact that the engine does not produce any blow-by gas by itself, the pressure regulators can regulate the crankcase pressure from the blow-by amount of air via the evacuation channels.
With airflow into the crankcase via the evacuation channels, a higher total flow is obtained through the oil separator, producing more complete oil separation. Furthermore, the increased blow-by gas velocity produces a higher heating effect in the gas, thereby improving the cold properties of the oil separator, pressure regulators and associated hoses and pipes.